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D e'; 2s, 1956 H. M. LAVENDER, JR

Filed Deo. 17, 1954 United States Parent Q M EXTRACTIVE msTrLLATIoN PRocEss Fon e RECQVERING AROMATICS 4 Harrison M. Lavender,Jr`., san Anselmo, Calif., assigner toCalifornia Research Corporation, San Francisco,

Calif., a corporation of Delaware Y Application December 17, 1954, seranA N6. 475,889

7claims. (ci. 26o-66s) land toluene from catalytic reformates, and it therefore will be particularly described hereinafter as it relates to said? process. t

p In producing the benzene and toluene-containing reformate streams to which this invention particularly relates,` a petroleum naphtha fraction consisting essen? tially of a mixture of naphthenic, parainic and aromatic hydrocarbonshaving from six to seven carbon atoms in` the` molecule is'contacted in the vapor phase with a platinum-alumina or other platinum-containing reformingA catalyst under suitable conversion conditions soy as largely to convert the4 naphthenic hydrocarbons'containing six carbon atoms to benzene and the seven carbon atom naphthenic hydrocarbons to toluene, the straight carbon chain parafnic hydrocarbons in the .feed being isomerized in part to branched-chain compounds. t

While the gaseous and other components of the reformate product obtained in this fashion which boil below hexane can readily be removed without appreciable'loss ofthe desired aromatic compounds, thisis not the case with the remaining nonaromatic contaminants which normally comprise from about 25 to 75% by volurne of the product remaining after removal of the lighter components. The problem of yrecovering benzene from the reformate is particularly acute, since the established specications for the'pure grade of benzene which must be recovered from vthe unit, if the process is to be operated in an economic fashion, are such as to permit the` presence of only trace amounts of other aromatic compounds as well as of nonaromatic contaminants. This is borneout by the fact that as little as 0.1% of toluene is suliicient to bring the boiling range to the limit of the i specification, which calls for a distillation range of 1 C.,

initial to dry.

Since the distillate fractions initially obtained following various petroleum reforming and other operations which are productive of aromatic product streams normally contain substantial amounts of at least one other aromatic compound than the desired product, along with various nonaromatic materials, the practice which is now followed by a large segment of the industry is to redistill such vfractions under rigorous conditions whereby a` fraction is obtained which contains the` desired aromatic. compound but is free of other aromatic contaminants. Thus, in the case of the benzene-containing fraction recovered from a catalytic reforming operation, which normally contains a substantial amount of toluene along with associated nonaromatic components, the practiceis to subject this` fraction to one or more preliminary fractional distillation steps designed to provide a benzene heartfcut ,whichis substantially free orf any toluene (less than 0.1% by volume, in terms of the benzene content),

2,775,627 l `Patented Dec. 25, 1956 and thereafter to subject this concentrate to an extractive distillation treatment whereby contaminating nonaromatic components are removed overhead, while the bottoms (which contain the benzene along with the extractive solvent) `are then distilled so as to recover substantially pure benzene. The foregoing method has the disadvantage that a heart cut which contains but a single aromatic compound and is free of contaminating aromatic components can only be obtained by a practice of the most exacting techniques involving the use of high retlux ratios and distillation columns containing as many as to 80 or more trays, thereby greatly adding to the cost of the recovery procedure.

While the marketing requirementsfor toluene are considerably less stringent than'those for the benzene component of the reformate, nevertheless the toluene-contain- In view of the foregoing difficulties, it would be de` sirable if a process Wereavailable which, while yielding benzene and toluene of the desired purity, Would at once eliminate Vthe need for effecting a substantially complete separation of the toluene from the benzene heart cut feed tothe extractive distillation zone, and also eliminate the need for redistilling the toluene-containing bottoms fraction recovered from the benzene heart cut still, and it is aj primary object of this invention to provide an improved method of this character.

The present invention is based upon the discovery that the foregoing objects are achieved by a procedure wherer' by the conversion product obtained by subjecting a suitable hydrocarbon feed stock to a catalytic conversion process productive of a reaction mixture containing benzene and toluene, along with various nonaromatic components, is first freed of gaseous and other relatively light constituents and is thereafter passed into a distillation column maintained under such conditions that the benzene is taken overhead in the form of a concentrate, or heart cut which includes from about 0.2,.to 10% toluene (in terms of the volume or benzene present) as well as various nonaromatic contaminants, while the balance of the toluene is recovered as a bottoms stream in such purity as to require no further redistillation in order to meet required standards. The benzene-containing concentrate is then introduced into an extractive distillation column to which a higher boiling extractive solvent (e. g., phenol) is also supplied, the conditions within this extractive distillation column being `such that a large proportion of the nonaromatic components are taken overhead, while the aromatic components of the feed, `along with any higher boiling nonaromatic components are withdrawn as bottoms. Said bottoms are then passed to a solvent stripping column operated under such conditions that the nonsolvent portions of the feed (containing the desired aromatics) are taken overhead and passed to anal fractionation column, while a stream made up essentially of solvent is withdrawn as bottoms and recycled back to the extractive distillation column. Quite unexpectedly, it has been found that even though the feed to said final distillation column contains appreciable quantities of toluene and nonaromatic contaminants, nevertheless the benzene can be distilled overhead in a high degree of purity (at least 99% benzene, and less than 0.1% of other aromatics, by volume), while recovering 4as bottoms a stream containing said toluene and v nonaromatics. The latter stream can then either be diverted for use as a component of motor gasoline, or it can be recycled back to the column from which the benzene heart cut is taken overhead and the toluene is withdrawn as bottoms.

While V.phenol has..been giventaboyeas an exampleiof.

an,e`xtr'active solvent,..and is, ,in fact, Vthe,p referredfsolvent for` use..in.thisinver 1tionwhen/recovering, benzene or toluene, .a wide variety of vothersolventstcanbeemployed.

Inigenerahthesolvent selected. shouldhavea boiling. point which isfwell vabove the endpoint :of thecstoclcfibeng, treated-.and which .can thus A.be readily,.separated. .from the dissolved components.A Thus, suitable solvents which can be employed in a practice of Athis.invention are; phenolaniline, .cresylic,aci,ds,` alkyl phenols, .various p olyglycols` including di.,V tril and. tetraethylene glycol, .,car.-

bitol's,` .di'ethanolamine nitrobenzene, quinoline, furfural` whereinthe ligure represents a flow diagram of-.a process.

for,..yrecovering pure. benzene, as well as a relatively pure toluene 4streannfrom apetroleum naphtha feed stock. In thegure, afeed mixture comprising a petroleum naphtha fraction consisting .primarily of a mixture of naphthenic, parainic .and aromatic hydrocarbons having .from sixto sevencarbon atomsin themolecule is passed at a rate of.' 1000 volumes per day through line,9v in the vapor phase .into .contact with a reforming catalyst in reforming zone. 10 undery elevated conditions. of temperature and pressure, suitable for et'fectingthe desiredconversion of.

theCsnaphthenes to benzene and the C7 naphthenes to toluene, andto largely isomerize the straight ,chainparainic hydrocarbons present to branched, chain. cornpounds. about.49. volumes of other gasesareremovedthrough line 11,while.the vbalance of the reformateipasses through line ,12 into a stabilizer column 13 provided Withv a suitable .reboiler 14,v from vwhich column. the lighter fractions comprising predominantly Cri-C4 hydrocarbons are taken overhead ata temperature of about 30 F. through line 15.and. condenser 16, with a portion of saidlighter hydrocarbons beingsent to productrecovery through line 17 at a rate of about .3 volumes per day, while the balance isreturned as reflux to the column through line 18.

A The bottoms-from stabilizer column 13 are withdrawn through line 19 and passed into .a topping still 20-provided witha reboiler 21. From this still a lighter fraction comprisingessentially C5 and C6 hydrocarbons boiling below hexane, is taken ,overhead at a temperatureof about .155 F.. through line 22fand condenser 23, with a portion of the condensate(2l5 volumes per day) being sent to product recovery through line24, while .the balance is returned.

amount-.equal-to `from, about 0.2 tol by volume,

basedton the benzene content of the. fraction, along with a substantialy proportion of nonaromatic components. Of thefresulti-ngVv condensate, a portion is returned to the columnas refluxthrough line 34 (reux ratio, 2:1), while theibalance of the streamy (485 `volumes per day) is passed throughflineSS into la mid-point of an extractive distillation-column 36'having a reboiler-38. l,The balance of the-toluene introducedy into rerun' column 30 through line- 26 is removedas bottoms'from'fsaid` column throughline 37nalongjwitha small percentage of 'hydrocarbons 'boil From the reforming zonehydrogen alongwith' 41. ing above benzene, at a rate of about 173 volumes per day.

In a representative run, the benzene concentrate in line 35 contains 50.3% benzene and 3.7% toluene, based on benzene, the balance being nonaromatics, While the bottoms stream in line 37 contains9,4.8% toluene and 5.2% nonaromatics.

Asistated'aboye; the-fb'enzene .concentrate isintroduced into column 361atthe ratetof '485:.volumesper day, and to this column. .phenol is added through .line 51 at. a rate of 1300' volumes perv day. In column 36,nonaromati'c ,hydrocarbons are taken overhead thr.,ough.line,39 andacondenser 40, with a portion being returned to the column as reuxthrouglsifA line= 42' (reiluxv ratio -4:-l);- while a raffinate stream amounting to 330.,.volumes per day is sent to a suitable recovery system (not shown) through line 41, said ranate, at a still head temperature of about 180 F., consistingpf 95.2% nonaromatics and but 4,8% benzene.KA

The bottoms from. the.column` 36, which contain the desired'benzene alongrwith associated -higher boiling aromatic' (toluene)`and nonaromatic contaminants` as well as solvent, are supplied' through line 43 at a temperature of about' 325?. E; to a midfpoint of a' stripping ycolumn44 providedfwith'a reboiler 45. From the column 44 (when operated, for example',` at a still head temperature of 200.F. and lat a reuxratio of about .2:1), an overhead stream ,consisting of 91.4% benzene, 3.5 toluene and 5:lf%` nonaromatics is taken over head through line 46 andcondenserj47, with aI portion beingreturned to theA columnas redux through 1ine48, while the balance is passedthrough line 49'atarate of`255 volumes per day to ajfractionating column.50.` The bottoms from the strippvingcolurnn,.44," which contain the extractive solvent alonglwithia smalLpercentage.oftoluene and of nonaromatics,1are withdrawn through line 511 at a temperature of abiout395 C.` andfrecycled back to the extractive dis'- till'ati'on column 36'at'a rate of 1300 volumes per day.

The'fractionating column 50, which is provided with al reboiler 52, is operatedat an overhead temperature of about 190"'F. and' at a reuxratio of'approximately 2:1. Fromjthis columnan overhead stream containing 99.2%' benzene;andiapproximately 0.8%.nonaromatics is taken overheadthroughline 53' and condenser 54 with a portion ofthestream beingh returned as reux through line 55,l While1-the.balan'ce`is Withdrawn .from the unit, ata rate of '233' volumes per day, through line 56. This substantially pprebenzene product may, if.desired, be passed to aA treatingljzone Where the material'is subjected to con- Ventional'nishing; treatments yrequired for the production offla productv of'nitration grade. A bottoms stream made upllvolumes of nonaromatics and 9 volumes of toluene is withdrawnzfrom column 4through line 57 at a ternperatureof about 240"F., thisproductbeing either sent totmotorgasoline storage, or. recycled back to column 30.

Iir theY foregoing description, the various percentages given-are'on a volume basis, and the volumes given refer-to the .product when in a liquid state. Further, in the flow diagram various ofthe required pumps, heat exchangers, valves'and other items of 'flow control equipment have been omitted'in the interests of simplicity and clarity`of expression, the placement of such auxiliary equipment` being :evident `to'those skilled in the art.

While'the :character of-this invention has `beendescribed in'detailand numerousillustrative examples` given, this hasbeen donebyway ofillustrationonly and' with the intentionthat no limitation-should beimposed upon the invention'th'ereby. It`will be apparent to thosev skilled in theart'that numerous modifications and variations may be effected'in thepractice of this invention which is of th'escope of the claimsy appended hereto.

1; Iiiraf process forjrecovering substantiallypurebenzeneN from a" catalytic-l reformate containing benzene; toluene-sandnonaromatic components; the^steps compris-A amasar ing freeing the reformate of normally gaseous and other lighter nonaromatic constituents; passing the remaining reformate product so obtained to a re-run column from which a benzene concentrate containing substantially all the benzene content of said reformate, along with nonaromatic components and an yappreciable amount of toluene, is taken overhead, and from which a fraction comprised in major portion of toluene is withdrawn as bottoms; passing said concentrate to an extractive distillation column, and there contacting the concentrate with a selective solvent at elevated temperatures whereby a substantial portion of the nonaromatic components are separated as an overhead product, while withdrawing a bottoms product containing substantially all of the benzene and toluene present in the concentrate, along with any remaining nonaromatic components` and solvent; passing said bottoms product to a solvent stripping column maintained at a temperature adapted to distill overhead the nonsolvent portions of the feed to the column while withdrawing as bottoms, and recycling to the extractiva distillation column, a solvent fraction which is low in nonsolvent components; passing the overhead from the solvent stripping column to a fractionating column maintained under such conditions as to distill the benzene overhead as a substantially pure benzene stream, while withdrawing as bottoms a fraction containing toluene and any remaining nonaromatic components, as present in the benzene concentrate.

2. The process of claim l wherein the solvent is phenol.

3. The process of claim 1 wherein the bottoms stream from the last-mentioned fractionation column is recycled to the re-run column.

4. In a process for producing and separating substantially pure benzene wherein a petroleum naphtha fraction consisting primarily of a mixture of naphthenic, parainic and aromatic hydrocarbons having six to seven carbon atoms in the molecule is passed into contact in the vapor phase with a reforming catalyst under suitable conversion conditions to largely convert the six carbon atom naphthenic hydrocarbons to benzene, the seven carbon atom naphthenic hydrocarbons to toluene and to largely isomerize the straight carbon chain paranic hydrocarbons present to branched-chain compounds, with the resulting catalytic conversion product being thereafter freed of normally gaseous and other lighter constituents present,

the improvement which comprises passing the remaining conversion product to a re-run column from which is taken overhead a benzene concentrate including substantially all the benzene present, together with nonaromatic components and a small percentage of toluene, and from which a fraction comprised in major portion of toluene is withdrawn -as bottoms; passing said benzene concentrate to an extractive distillation column, and there contacting the concentrate with a selective solvent at elevated temperatures whereby a substantial portion of the nonaromatic components are separated as an overhead product, while withdrawing a bottoms product containing substantially all of the benzene and toluene present in the concentrate, along with any remaining nonaromatic components and solvent; passing said bottoms product to a solvent stripping column maintained at a temperature adapted to distill overhead the nonsolvent portions of the feed to the column while wthdrawing as bottoms, and recycling to the extractive distillation column, a solvent fraction which is low in nonsolvent components; passing the overhead from the solvent stripping column to a fractionating column maintained under such conditions as to distill the benzene overhead as a substantially pure benzene stream, while withdrawing as bottoms a fraction containing toluene and any remaining nonaromatic components, as present in the benzene concentrate.

5.` The process of claim 4 wherein the bottoms from the last-mentioned fractionating column are recycled to the re-run column.

6. The process of claim 4 wherein the overhead from the re-run column contains from about 0.2 to 10 volume percent toluene, based on the amount of benzene present, and wherein the bottoms from said column contain at least volume percent toluene.

7. The process of claim 6 wherein the solvent is phenol.

References Cited in the le of this patent UNITED STATES PATENTS 2,409,695 Laughlin Oct. 22, 1946 OTHER REFERENCES Dunn et al.: The Oil 8: Gas Journal, June 9, 1952,V

pages 68-70 and 96. 

1. IN A PROCESS FOR RECOVERING SUBSTANTIALLY PURE BENZENE FROM A CATALYTIC REFORMATE CONTAINING BENZENE, TOLUENE AND NONAROMATIC COMPONENTS, THE STEPS COMPRISING FREEING THE REFORMATE OF NORMALLY GASEOUS AND OTHER LIGHTER NONAROMATIC CONSTITUENTS; PASSING THE REMAINING REFORMATE PRODUCT SO OBTAINED TO A RE-RUN COLUMN FROM WHICH A BENZENE CONCENTRATE CONTAINING SUBSTANTIALLY ALL THE BENZENE CONTENT OF SAID REFORMATE, ALONG WITH NONAROMATIC COMPONENTS AND AN APPRECIABLE AMOUNT OF TOLUENE, IS TAKEN OVERHEAD, AND FROM WHICH A FRACTION COMPRISED IN MAJOR PORTION OF TOLUENE IS WITHDRAWN AS BOTTOMS; PASSING SAID CONCENTRATE TO AN EXTRACTIVE DISTILLATION COLUMN, AND THERE CONTACTING THE CONCENTRATE WITH A SELECTIVE SOLVENT AT ELEVATED TEMPERATURES WHEREBY A SUBSTANTIAL PORTION OF THE NONAROMATIC COMPONENTS ARE SEPARATED AS AN OVERHEAD PRODUCT, WHILE WITHDRAWING A BOTTOMS PRODUCT CONTAINING SUBSTANTIALLY ALL OF THE BENZENE AND TOLUENE PRESENT IN THE CONCENTRATE, ALONG WITH ANY REMAINING NONAROMATIC COMPONENTS AND SOLVENT; PASSING SAID BOTTOMS PRODUCT TO A SOLVENT STRIPPING COLUMN MAINTAINED AT A TEMPERATURE ADAPTED TO DISTILL OVERHEAD THE NONSOLVENT PORTIONS OF THE FEED TO THE COLUMN WHILE WITHDRAWING AS BOTTOMS, AND RECYCLING TO THE EXTRACTIVE DISTILLATION COLUMN, A SOLVENT FRACTION WHICH IS LOW IN NONSOLVENT COMPONENTS; PASSING THE OVERHEAD FROM THE SOLVENT STRIPPING COLUMN TO A FRACTIONATING COLUMN MAINTAINED UNDER SUCH CONDITIONS AS TO DISTILL THE BENZENE OVERHEAD AS A SUBSTANTIALLY PURE BENZENE STREAM, WHILE WITHDRAWING AS BOTTOMS A FRACTION CONTAINING TOLUENE AND ANY REMAINING NONAROMATIC COMPONENTS, AS PRESENT IN THE BENZENE CONCENTRATE. 